Remove note: scrollbar-width property is at risk of being removed

No longer true, see w3c/csswg-drafts#1958 (comment)

features-json/css-scrollbar.json

@@ -409,7 +409,6 @@
       "2.5":"n"
     }
   },
-  "notes":"scrollbar-width property is at risk of being removed see [Issue 1958 on CSSWWG-Drafts](https://github.com/w3c/csswg-drafts/issues/1958)",
   "notes_by_num":{
     "1":"Only supports styling scrollbar colors through proprietary prefixed properties, no other properties to define the scrollbar's appearance. (not on standards track)",
     "2":"Supports scrollbar styling via CSS [pseudo-properties](https://webkit.org/blog/363/styling-scrollbars/). (not on standards track)",